Lyme disease, a tick-borne infection caused by the spirochete Borrelia burgdorferi, has expanded to an estimated 300,000 US cases per year. Currently approved tests of immune response are sub-optimal and often give negative results early in the disease. The research outlined in this application is to develop a diagnostic blood test that directly visualizes B. burgdorferi. This test will allow earlier detection - and hence beter treatment - and could be used to monitor symptomatic patients for response to treatment. RareCyte Inc., an early-stage life science company dedicated to the characterization and retrieval of rare cells in blood, has a highly engineered enrichment technology based on a tube, float and collection mechanism that can stratify cells and pathogens in the blood by density. Using this technology, a prototype assay has been developed that has demonstrated direct visualization of B. burgdorferi antigen- positive organisms by immunofluorescence microscopy in cultured spirochetes, spiked- in blood samples, and in blood of patients with early Lyme disease. The long-term goal of this project is to make commercially available a sensitive and specific direct visualization laboratory test for Lyme disease with demonstrated clinical utility. We hypothesize that the direct detection visualization assay will reliably and specifically identif Borrelia spirochetes in the blood at a low limit of detection. Specifically, we will: (1) optimize nd validate technical performance of the assay and achieve target sensitivity of 80% at 2 organisms per mL; (2) evaluate background signal and perform a spike-in study in blood samples from non-endemic subjects to define a positive cut-off with 90% specificity, and establish intra- and inter-laboratory reproducibility of 85%; (3) investigate clinical performance characteristics of the assay in a pilot study to include samples from patients before, during and after Lyme disease antibiotic treatment. We expect to achieve an optimized and validated assay with defined scoring criteria and control reagents to directly detect B. burgdorferi in blood for ue in a Phase II multi-laboratory, blinded clinical validation study to demonstrate equivalence or improved performance over current two-tiered testing. The market for the assay parallels the high incidence of Lyme disease, and is estimated at between 1 and 2 million tests per year. RareCyte will develop licensing and partnering strategies to provide kits and instruments for FDA 510(k) approval.